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Highlights • Mechanical stress induced by the striction of MR composites is experimentally studied. • Composites with magnetic soft and magnetic hard filler are considered. • Effect of the structuring and pre-magnetization of the composites is evaluated. • The magnitude of the strictional effect is related to the magnetic susceptibility of the composite. Abstract In this study we experimentally examine the mechanical stress induced by the striction of hybrid magnetoactive elastic composites in the direction parallel to an externally applied magnetic field. Elastic samples based on a polydimethylsiloxane matrix with embedded spherical magnetic soft carbonyl iron particles, spherical magnetic hard NdFeB-alloy particles as well as on a mixture of the two kinds of powder are under investigations. An effect of the structuring and pre-magnetization of the samples on the stress induced by the magnetodeformational effect is evaluated. [ABSTRACT FROM AUTHOR]

Abstract For the first time excitation and luminescence spectra of Mn2+ ions in β-PbF 2 crystals at 77 and 300 K, and also the luminescence lifetime are studied. Impurity ions in the crystal form a cubic center and centers of lower symmetry, and also exchange-coupled pairs. The origin of the formation of noncubic centers during the substitution Mn2+ → Pb2+ are the large difference of ionic radii Mn2+(0.80 Å) and Pb2+ (1.26 Å) creating the instability of the local structure around the activator ion, its deformation, and exchange striction. The increase in the impurity concentration enhances these factors leading to the change of the relative concentration of different centers. The strong manifestation of the Jahn-Teller (Ham) effect is found in the luminescence excitation spectra. The importance of using the Trees-Racah α and seniority β corrections in the scheme of the crystal field theory (CFT) calculations is demonstrated. The connection between Trees-Racah corrections values and symmetry of Mn2+ surrounding in homologous crystals Me F 2 (Me = Ca, Sr, β – PbF 2 , Ba) has been revealed. Highlights • Multiple centers of Mn2+ ions in β–PbF 2 crystal luminescence is studied. • Models of pair-centers of Mn2+ ions in β–PbF 2 crystal are proposed. • Energies of transitions in Mn2+ ions in β–PbF 2 crystal are calculated. [ABSTRACT FROM AUTHOR]

ABSTRACT Polypropylene/multiwall carbon nanotube nanocomposites with different rates of weight incorporation (0-1%) were prepared by melt compounding and cast extrusion. The effect of maleic anhydride (5 wt%) grafted on polypropylene is studied through mechanical tests at different scales and morphological observations. In particular, the micromechanism of deformation was investigated through instrumented tensile experiments (at a macro and micro scales) using of a non-contact method known as digital image correlation. The objective of this paper is first to characterise global behaviour (Young modulus, tensile strength, and ultimate properties) and second to go further in local analysis. In particular, optical instrumentation enables estimation of strain profile distribution onto the sample in a constricted area. Statistical parameters extracted from these local profiles are promising tools to enhance mechanical properties in link with microstructural composition. Tensile tests confirm composite reinforcement at a low level of nanocomposite incorporation, and local analysis enables quantitative measurements of adding maleic anhydride in formulations. The results reveal that addition of maleic anhydride delays strain localisation in the necked area. [ABSTRACT FROM AUTHOR]

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• Parametrically amplified harvesting of ambient field energy for wireless sensor hub. • Parametric excitations in a single mode Helmholtz-Duffing oscillator. • Nonlinear stress-strain curves achieved through field-induced striction. • Increased achievable broadband power of vibrational energy harvester. We investigate the influence of parametric excitations on MEMS vibration energy harvesters for energy autonomous sensor systems. In Industry 4.0 (or Industrial IoT) applications, interconnected sensors provide a means of data acquisition for automated control of the manufacturing process. Ensuring a continuous energy supply to the sensors is essential for their reliable operation. Manufacturing machines usually display a wide spectrum of vibration frequencies which needs to be covered by an array of harvester substructures in order to maintain the desired output level. We show that mechanical structures designed to implement a Helmholtz-Duffing oscillator have an increased bandwidth by exploiting several orders of parametric resonances. In contrast to concepts implementing parametric amplification in a multi-mode scenario, our concept is based on a single mechanical mode. Therefore, it is more robust against fabrication tolerances as the relevant multi-mode resonance conditions do not need to be matched on the level of single chips. Using exact transient simulations and semi-analytic models to showcase the relation of the Helmholtz-Duffing oscillator to the damped and driven Mathieu equation, we show that parametric resonances highly increase the bandwidth of the output power whenever high Helmholtz nonlinearities are present. To achieve the required nonlinearities, we suggest nonlinear stress-strain curves and we propose to achieve such nonlinearities through field-induced striction by magneto- or electrostriction. In contrast to existing approaches, where external fields are harvested using strictive effects, we employ external fields that manipulate the effective Young's modulus to achieve parametric excitations in a mechanical oscillator. Thus, we are able to propose a novel energy harvester concept incorporating strictive materials that exploits the effects of parametric excitations to achieve broadband vibrational energy harvesting. [ABSTRACT FROM AUTHOR]